1. Field of the Invention
The present invention relates to a process for producing ellagic acid.
2. Description of the Prior Art
Ellagic acid is a polyphenolic compound widely distributed in plants in the natural world. In plants, ellagic acid after exists as one of constituents of tannins called ellagitannins, though it exists also in free state.
Ellagic acid is known to have a powerful blood clotting effect and is utilized for separation of serum in
the field of clinical chemistry [Jap. Pat. Appln. Kokai (Laid-Open) No. 60-27858].
In addition, ellagic acid is used as an antioxidant for goods by taking advantage of its anti-oxidizing ability [Jap. Pat. Appln. Kokai (Laid-Open) No. 60-15486].
Furthermore, ellagic acid has been found to have anti-mutagenic activity and is expected to be utilizable as a preventive against cancer. Thus, ellagic acid is a useful substance which can be widely utilized in the field of foods, medicines and medical treatment.
Ellagic acid has heretofore been produced, for example, by the following processes.
1 A process in which ellagic acid is produced by decomposing an ellagitannin with an acid [Jurd, J. Am. Chem. Soc. 78. 3445 (1956) and 79, 6043 (1957)].
2 A process in which ellagic acid is isolated from a dipped liquid of pulps such as eucalyptus, etc. [Jap. Pat. Appln. Kokai (Laid-Open) No. 51-63921].
3 A process in which ellagic acid is produced by oxidative polymerization of gallic acid or an ester thereof (methyl gallate, ethyl gallate or the like) [Mayer W. et al., Liebigs Ann. Chem., 929 (1984); Hathway D. E., Biochem. J. 67, 445 (1957); and Kamel, M. Y. et al., Phytochemistry 16, 521 (1977)].
However, the process of is 1 attended with danger, for example, a high temperature is required for the acid decomposition. In the process of 1, the yield of ellagic acid is relatively high (about 40%), but the process is very complicated in extraction of ellagitannin from raw materials such as the bark of chestnut, etc. In the process 2, the yield of ellagic acid from pulps is low (about 1.0%) and hence the process 2 is not practical.
On the other hand, the process of 3 is not always advantageous because a process for preparing the starting material, i.e., gallic acid is long and complicated. In the process of 3, the yield of ellagic acid is approximately 20-30% which is not satisfactory enough.